Modify //sdk:create_common_sdk to choose which devtools to include

[srawlins]

See https://dart.googlesource.com/sdk/+/27952c536839aee47e8d2f8a898c692f666dd541/sdk/BUILD.gn#812. Depending on build_devtools_from_sources from the .gclient file, it can use either cipd or locally built devtools.