Fix systemd sysconfig files for nfs-ganesha

Consolidate two files into one and modify install scripts to pick right
sysconfig file.

Signed-off-by: Venkateswararao Jujjuri (JV) <jvrao@linux.vnet.ibm.com>
Acked-by: Allison Henderson <achender@vnet.linux.ibm.com>
Acked-by: Malahal Naineni <malahal@us.ibm.com>