adb start doesn't work on Linux

[jmarcgit]

Hi,

I had a look at the source code and it looks like that the automatic adb startup only works for Windows machines when the ANDROID_HOME env variable is set. (note that ANDROID_SDK_ROOT replaced ANDROID_HOME lately)

I think it could make sense to add an adbPath parameter to the extension. For instance in Debian you can install the adb command without installing the full SDK. Setting adbPath:adb would just work in that case.

Or of course you could consider to support Linux like systems building the adb path from the env variable. I think you would prefer this solution.