ci: Detect shell prompt with higher specificity

The current pattern '#' triggers on the openSUSE kernel version that is
printed early during boot when no actual prompt is ready
> [    0.000000] Linux version 5.12.10-1-default (geeko@buildhost) (gcc (SUSE Linux) 11.1.1 20210510 [revision 23855a176609fe8dda6abaf2b21846b4517966eb], GNU ld (GNU Binutils; openSUSE Tumbleweed) 2.36.1.20210326-4) #1 SMP Fri Jun 11 05:05:06 UTC 2021 (b92eaf7)

Instead wait for pattern that: a) should have fewer false positives, b)
still be with working on distro shells:

openSUSE (red color)
^[[1m^[[31mimage:~ #^[[m^O

arch
[root@image ~]#

debian
root@image:~#

ubuntu
root@image:~#

fedora
[root@image ~]#