Merge pull request #17720 from KevinGrandon/bug_864178_test_agent_sandboxing

Bug 864178 - [TestAgent] Run each test in its own sandbox
(cherry picked from commit 57c273a5d7fb9da8a4299964a8f54ad5a709436c)
Merge pull request #17800 from KevinGrandon/bug_989916_captive_portal_test_sandboxing

Bug 989916 - [System] Fix captive_portal_test.js when run in its own sandbox
(cherry picked from commit 77a873e591bb8261130e752ba5f19164b1e23198)
Merge pull request #17729 from KevinGrandon/bug_989065_wifi_test_sandbox

Bug 989065 - [System] Fix wifi_test.js when run in its own sandbox r=alive
(cherry picked from commit a47b03757d14af9832cf34a59a6871c353a493b5)
Merge pull request #17724 from KevinGrandon/bug_989019_calendar_test_sandbox

Bug 989019 - [Calendar] Fix alarm_test.js when run in its own sandbox
(cherry picked from commit 39b307f67e8945f6ec458e72c8734c907413b14e)
Bug 864178 - (1.4 only) Fix some tests depend on other scripts
Merge pull request #21324 from timdream/sandbox-test-v1.4

Bug 864178 v1.4 uplift +shepherd a=tests r=julien