tests: break out command, command/agent on Travis

The command and command/agent packages are taking 5+ minutes on Travis
and this contributes to build timeouts. While this doesn't address
underlying issues, breaking these out can reduce re-runs until that
work is done.

.travis.yml

@@ -28,6 +28,16 @@ matrix:
       sudo: required
       env: GOTEST_PKGS="./client"
       <<: *skip_for_ui_branches
+    - os: linux
+      dist: xenial
+      sudo: required
+      env: GOTEST_PKGS="./command" GOTEST_PKGS_EXCLUDE="./command/agent"
+      <<: *skip_for_ui_branches
+    - os: linux
+      dist: xenial
+      sudo: required
+      env: GOTEST_PKGS="./command/agent"
+      <<: *skip_for_ui_branches
     - os: linux
       dist: xenial
       sudo: required
@@ -46,7 +56,7 @@ matrix:
     - os: linux
       dist: xenial
       sudo: required
-      env: GOTEST_PKGS_EXCLUDE="./api|./client|./drivers/docker|./drivers/exec|./nomad"
+      env: GOTEST_PKGS_EXCLUDE="./api|./client|./command|./command/agent|./drivers/docker|./drivers/exec|./nomad"
       <<: *skip_for_ui_branches
     - os: linux
       dist: xenial