add Jenkinsfile to test each PR and branch commits

This includes a basic test that attempts to compile the rustfmt crate.
Ensures that the workspace is always removed at the end of the build. It
utilizes available caches to speed up the build process and parallelizes
the build across i386, x86_64, arm32, and arm64 targets.

Signed-off-by: Derek Straka <derek@asterius.io>

conf/local.conf.sample

@@ -220,6 +220,10 @@ BB_DISKMON_DIRS = "\
 #file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=PATH \n \
 #file://.* file:///some/local/dir/sstate/PATH"
 
+SSTATE_MIRRORS ?= "file://.* http://build-cache.asterius.io/sstate/PATH;downloadfilename=PATH \n"
+
+SOURCE_MIRROR_URL ?= "http://build-cache.asterius.io/downloads/"
+INHERIT += "own-mirrors rm_work"
 
 #
 # Qemu configuration