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.

libvirt cannot fix this in time for their impending release. This is
submitted to gerrit to provide some minimal visibility upstream to justify
hacking this change (as a temporary patch) into the glusterfs-3.4.1 RPMs
for Fedora 18-21 until libvirt can fix their implementation.

Change-Id: Ie77b00ac60730d1e48907dd0b38ddae92f3ac345
BUG: 987555
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/6147
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavan Pichai <rpichai@redhat.com>