oeqa: qemurunner: Report UNIX Epoch timestamp on login

oeqa: qemurunner: Report UNIX Epoch timestamp on login

Updates the log message printed when login banner is seen in QEMU to
report the UNIX Epoch time in addition to the human readable time. This
makes it much easier and accurate to correlate logs with the guest, in
particular with the guest journalctl which prints log timestamps in
human readable format and the oeqa SSH debug logging which prints the
UNIX Epoch.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>