SDK Manager: env var SDK_TEST_BASE_URL. Do not merge.

Support a new env var SDK_TEST_BASE_URL that should
be set to the root of an alternate repo. When set
it will completly override the built-in default
repository base URL.

(cherry picked from commit b0ac9620f74f0b3817a8847178ca53d876b78a09)

Change-Id: I029d322a22b6c24c14880c8ffcf8529198bbebde
4 files changed