cpanm: search both its stderr and its stdout for the message 'is up t…

Note that since cpanm version 1.6926 its messages are sent to stdout
when previously they were sent to stderr.

Also there is no need to initialize out_cpanm and err_cpanm and
check for their truthiness as module.run_command() and str.find()
take care of that.

lib/ansible/modules/extras/packaging/language/cpanm.py

@@ -202,7 +202,6 @@ def main():
     installed = _is_package_installed(module, name, locallib, cpanm, version)
 
     if not installed:
-        out_cpanm = err_cpanm = ''
         cmd       = _build_cmd_line(name, from_path, notest, locallib, mirror, mirror_only, installdeps, cpanm, use_sudo)
 
         rc_cpanm, out_cpanm, err_cpanm = module.run_command(cmd, check_rc=False)
@@ -210,7 +209,7 @@ def main():
         if rc_cpanm != 0:
             module.fail_json(msg=err_cpanm, cmd=cmd)
 
-        if err_cpanm and 'is up to date' not in err_cpanm:
+        if (err_cpanm.find('is up to date') == -1 and out_cpanm.find('is up to date') == -1):
             changed = True
 
     module.exit_json(changed=changed, binary=cpanm, name=name)