Add protocol v2 support in "jgit daemon"

Add protocol v2 support in "jgit daemon"

With this patch, a server spawned by "jgit daemon" can be accessed using
protocol v2 from a Git client that supports it (for example, "git" with
the appropriate patches). This is only activated if the repository's
config has "protocol.version" be 2.

This required a change to the package-private #execute methods in
DaemonService to allow passing of extra parameters.

This has been tested with a patched Git.

Change-Id: Icf043efec7ce956d72b075fc6dc7a87d5a2da82a
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>