fix multithreaded create()

We were calling save_config() twice within the create() flow, each
from a different process. Depending on order of scheduling, sometimes
the data from the first save_config() (which was just the stuff from
LXC_DEFAULT_CONFIG) would overwrite the config we wanted (the full
config), causing a truncated config file which would then cause lxc
to segfault once it read it back in because no rootfs.path was set.

This fixes it by only calling save_config() once in the create()
flow. A rejected alternative was to call fsync(fileno(fout)) before
the fclose in save_config.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: S.Çağlar Onur <caglar@10ur.org>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
add process_lock()/unlock() in save_config()

This is likely unnecessary, but is consistent with other uses of
fopen()/fclose() in lxc.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: S.Çağlar Onur <caglar@10ur.org>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>