Remove unnecessary directory push/pop from scripts

This commit proposes removing an unnecessary directory push/pop from the
X-Pack scripts. It is not clear exactly why these were added, the
original change was almost three years ago in
elastic/x-pack@ea9ba7cdd0 but
unfortunately the commit message does not elucidate the exact the
problem, nor is there an associated pull request. This change has
propogated into all of the X-Pack scripts yet still the reasons are
unclear. The little that we can glean from the commit message is that
there was a problem with the default paths if the script was executed
outside of the Elasticsearch home. It seems that such issues have been
addressed by the recent introduction of elasticsearch-env so maybe we
can simplify these scripts here?

Relates elastic/x-pack-elasticsearch#2125

Original commit: elastic/x-pack-elasticsearch@9548c47743

plugin/bin/x-pack/certgen

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.ssl.CertificateTool \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/croneval

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.watcher.trigger.schedule.tool.CronEvalTool \
   "$@"
-  
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/extension

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.extensions.XPackExtensionCli \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/migrate

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.security.authc.esnative.ESNativeRealmMigrateTool \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/setup-passwords

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.security.authc.esnative.tool.SetupPasswordTool \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/syskeygen

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.security.crypto.tool.SystemKeyTool \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status

plugin/bin/x-pack/users

@@ -8,16 +8,11 @@ source "`dirname "$0"`"/../elasticsearch-env
 
 source "`dirname "$0"`"/x-pack-env
 
-cd "$ES_HOME" > /dev/null
-
-"$JAVA" \
+exec \
+  "$JAVA" \
   $ES_JAVA_OPTS \
   -Des.path.home="$ES_HOME" \
   -Des.path.conf="$CONF_DIR" \
   -cp "$ES_CLASSPATH" \
   org.elasticsearch.xpack.security.authc.file.tool.UsersTool \
   "$@"
-
-status=$?
-cd - > /dev/null
-exit $status