.oniro-ci: add oe-selftest dockerfile

The docker image is based bitbake-builder. 'sudo su - builder' step added for
oe-selftest as 'USER builder' doesn't really load user level profile. The below
vars are misssing before user re-switch.

  SHELL=/usr/bin/bash
  LOGNAME=builder
  LESSCLOSE=/usr/bin/lesspipe %s %s
  LESSOPEN=| /usr/bin/lesspipe %s
  USER=builder
  MAIL=/var/mail/builder

And PATHes are different before and after user re-switch.
Before: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
After: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin

Although 'whoami' command can be found in both PATHes, oe-selftest reports
'whoami' not found issue with the former path, the reason behind is to be
investigated. In general, user instead of root profile should be used for
oe-selftest.

Signed-off-by: Chase Qi <chase.qi@linaro.org>

.oniro-ci/containers/oe-selftest/Dockerfile

+FROM chaseqi/bitbake-builder:v1.3
+
+# 'USER builder' doesn't really load user level profile.
+# The below vars are misssing before user re-switch.
+# SHELL=/usr/bin/bash
+# LOGNAME=builder
+# LESSCLOSE=/usr/bin/lesspipe %s %s
+# LESSOPEN=| /usr/bin/lesspipe %s
+# USER=builder
+# MAIL=/var/mail/builder
+# And PATHes are different before and after user re-switch.
+# Before: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+# After: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
+# Although 'whoami' command can be found in both PATHes, oe-selftest reports
+# 'whoami' not found issue with the former path, the reason behind is to be
+# investigated. In general, user instead of root profile should be used for
+# oe-selftest.
+ENTRYPOINT sudo su - builder