jenkins: remove build history directory before collecting srcrevs

Signed-off-by: Marc Mattmueller <marc.mattmueller@netmodule.com>

Jenkinsfile

@@ -271,7 +271,7 @@ def getTopUpstreamBuildNumber() {
 }
 
 def getAutoRevHashes() {
-  sh(script: "bash -c '. ./env.image-ostree && bitbake netmodule-linux-image-dev --runall=fetch'")
+  sh(script: "bash -c '. ./env.image-ostree && rm -rf buildhistory && bitbake -f netmodule-linux-image-dev --runall=fetch'")
   def revs = sh(returnStdout: true, script: "bash -c \". ./env.image-ostree > /dev/null && buildhistory-collect-srcrevs\"").trim()
   return revs
 }