sysroot: Add dryrun option to InstallPackages endpoint.

Allow calls from the Build API to invoke the build_packages script with
the pretend flag.

BUG=b:189336144
TEST=./run_tests

Change-Id: Ib8901e50bc5c8467cb6b7198656f20a2ffdcb993
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2919899
Reviewed-by: Sean McAllister <smcallis@google.com>
Tested-by: Navil Perez <navil@google.com>
Commit-Queue: Navil Perez <navil@google.com>
diff --git a/api/controller/sysroot_unittest.py b/api/controller/sysroot_unittest.py
index dc6e03d..f28fc0d 100644
--- a/api/controller/sysroot_unittest.py
+++ b/api/controller/sysroot_unittest.py
@@ -612,7 +612,8 @@
         use_flags=[],
         use_goma=False,
         incremental_build=False,
-        setup_board=False)
+        setup_board=False,
+        dryrun=False)
 
   def testSuccessWithGomaLogs(self):
     """Test successful call with goma."""