This commit refactors instances of 'elasticsearch' with opensearch everywhere
except references to issues, and other places needed to test compatibility with
old elasticsearch clusters.
Signed-off-by: Nicholas Walter Knize <nknize@apache.org>
The system level tests for our distributions have historically be run in
vagrant, and thus the name of the gradle project has been "vagrant".
However, as we move to running these tests in other environments (eg
GCP) the name vagrant no longer makes sense. This commit renames the
project to "os" (short for operating system), since these tests ensure
all of our distributions run correctly on our supported operating
systems.