libexport.a: Allow m_hostname allocation to fail instead of exit

libexport.a: Allow m_hostname allocation to fail instead of exit

Clean up: Replace xstrdup() with strdup(3) in client_init(), to
prevent the process from exiting if the memory allocation fails.

Note that both of client_init()'s callers set m_hostname equal to NULL
before calling, thus the extra free(3) at the top of client_init() is
unneeded.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>