CLI: Add support for excluding paths from Git log command

CLI: Add support for excluding paths from Git log command

Git log supports the exclude pathspec, which allows for excluding paths
from the log command. JGit only supports adding paths to the log
command. See the following StackOverflow question for details:
https://stackoverflow.com/questions/59143934/java-jgit-how-to-get-git-
commits-not-affecting-certain-directories
This commit adds an excludePath() method to the log command. It does not
yet support regex or glob wildcards.

Change-Id: I8cd59950b87850b55a15c7e2ea5470145c9aae28
Signed-off-by: John Tipper <john_tipper@hotmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>