Returning iOS Version number in capabilities

Fixes #1332
Merge pull request #1527 from penguinho/ios_version

Returning iOS Version number in capabilities
Making default iOS version a string in the capabilities object
Fix 4-inch 64-bit device string building (was missing dash in 64 inch).
Merge pull request #1537 from curtissiemens/master

Fix 4-inch 64-bit device string building (was missing dash in 64 inch).
fail with a nice error message if xcrun can't find instruments (fix #1538)
fix at least one case of ios sims not being killed
cc @penguinho