Generate javadoc from a project in a subdirectory

Generate javadoc from a project in a subdirectory

Lift the assumption that all files are in the git repository root.
Extend maven-javadoc publish and javadoc-verify macros with mvn-dir
configuration parameter (like tox-dir), defaults to '.' to preserve
existing behavior.
Extend maven-javadoc-generate.sh script to invoke mvn with the -f
option and use the directory name when archiving the generated HTML;
drop -x setting to conform with other scripts.
Document the new configuration parameter.

Projects using macros lf-maven-javadoc-publish, lf-maven-javadoc-verify
(i.e., using job templates gerrit-maven-javadoc-publish,
github-maven-javadoc-publish, gerrit-maven-javadoc-verify or
github-maven-javadoc-verify) must ensure the maven -f option is not
used in config parameter mvn-params.

Change-Id: Ib02a12a3192b8be577a0367476628c46db333231
Issue-ID: RELENG-1872
Signed-off-by: Lott, Christopher (cl778h) <cl778h@att.com>