LFS: Dramatically improve checkout speed with SSH authentication

LFS: Dramatically improve checkout speed with SSH authentication

SSH Authentication is quite expensive (~120ms on localhost against
Gerrit with LFS plugin). The SSH authentication typically also sends a
validity time of the returned token, which allows to re-use it for a
certain time, avoiding the expensive authentication on every download
request. This improves checkout times by large factors depending on the
LFS object amount/sizes.

Also make sure that all instances of Gson used by LFS are configured in
the same way.

Change-Id: I422c94c37021b4322789b3829fa0185e25d683f2
Signed-off-by: Markus Duft <markus.duft@ssi-schaefer.com>