terminal.py: fixes launching multiple windows of gnome-terminal

When resolving a patch, a new process of gnome-terminal
is created for every patch to be resolved, it "waits"
for the previous one to end, instead of launching
multiple windows at the same time.

[YOCTO #7254]

Signed-off-by: Alejandro Hernandez <alejandro.hernandez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>