This commit removes the ability to specify that a plugin requires the
keystore and instead creates the keystore on package installation or
when Elasticsearch is started for the first time. The reason that we opt
to create the keystore on package installation is to ensure that the
keystore has the correct permissions (the package installation scripts
run as root as opposed to Elasticsearch running as the elasticsearch
user) and to enable removing the keystore on package removal if the
keystore is not modified.
This commit moves the distribution specific tasks into the respective
archives and packages builds. The collocation of common and distribution
specific tasks make it much easier to reason about what is expected in a
particular distribution.
This commit adds intermediate gradle projects for archive based
distributions (zip, tar) and package based distributions (rpm, deb). The
grouping allows the common distribution build file to be considerably
shorter and clearly separated from the common zip/tar and rpm/deb
configuration.