Fix activity detection

The old logic was completely broken.

The pkg must not be prepended to the activity. This is invalid.
shell am start -n
com.thehomedepot/com.thehomedepot..Foundation.Controller.SetServicesActivity

The activity must not have the first bit chopped off. This is invalid:
Foundation.Controller.SetServicesActivity

The correct command is adb shell am start -n
com.thehomedepot/.Foundation.Controller.SetServicesActivity

Notice there's no prepended activity and that the string after the / starts with
a "."

Fixes #782
Selendroid is unable to start some apps
Fix Cannot read property 'value' of undefined
Fix selendroid start

Wrong:
adb shell am instrument -e main_activity
'com.thehomedepot..Foundation.Controller.SetServicesActivity'
com.thehomedepot.selendroid/io.selendroid.ServerInstrumentation

Fixed:
adb shell am instrument -e main_activity
'com.thehomedepot.Foundation.Controller.SetServicesActivity'
com.thehomedepot.selendroid/io.selendroid.ServerInstrumentation
Merge pull request #785 from bootstraponline/782

Fix activity detection