terminal.py: use unique ids for screen sessions

terminal.py: use unique ids for screen sessions

When running multiple sets of builds on the same
system, it is hard to distinguish which build belongs
to which screen session and you can end up resuming
the wrong session.

The simple solution is to just append the process
id to the screen session invocation to make each
unique.

(From OE-Core rev: 1677b736bca5dc46db522da1874459d2de77209d)

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>