mgmt/glusterd: add option to specify a different base-port

This is (arguably) a hack to work around a bug in libvirt which is not
well behaved wrt to using TCP ports in the unreserved space between
49152-65535. (See RFC 6335)

Normally glusterd starts and binds to the first available port in range,
usually 49152. libvirt's live migration also tries to use ports in this
range, but has no fallback to use (an)other port(s) when the one it wants
is already in use.

Change-Id: Id8fe35c08b6ce4f268d46804bbb6dddab7a6b7bb
BUG: 1018178
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/6210
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>