jenkins.sh: cleanup always the workspace
jenkins.sh: cleanup always the workspace

It was broken before becaues of checking emptyness against literal string
will never be zero.
However it should be cleaned always because the script is executed
recursive which would also end up, never being executed.

Change-Id: Ib228ff247a72b21b12e8dd4cbe3afe3e858c89d3

ttsou/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx,ttsou/osmo-trx,osmocom/osmo-trx