ktest.pl: If size of log is too big to email, email error message

If the size of the error log is too big to send via email, and the sending
fails, it wont email any result. This can be confusing for the user who is
waiting for an email on the completion of the tests.

If it fails to send email, then try again without the log file stating that
it failed to send an email. Obviously this will not be of use if the sending
of email failed for some other reasons, but it will at least give the user
some information when it fails for the most common reason.

Cc: stable@vger.kernel.org
Fixes: c2d84ddb

 ("ktest.pl: Add MAIL_COMMAND option to define how to send email")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>