Changes

jenkins-common: support {latest,master}-debian10

It is required that we run the FR tests with debian 10. Adjust
jenkins-common.sh so we can use IMAGE_SUFFIX=master-debian10 and
IMAGE_SUFFIX=latest-debian10.

The related osmo-ci patch will configure jenkins to make use of this.

Related: OS#6494#note-19
Related: osmo-ci Ibd4cb705048ef5c39fa4192870e2b0f0d067842f
Change-Id: I1a41ca8ddd06f716c4bf29d60a0c2f0f82dc4e35