Only try to push if build doesn't fail

[jansepar]

Currently, if there is an issue with a build we still try and push it, which will fail because the bld folder will be removed. This should be fixed. Here is an example of an error log for this issue:

mobify push --message "RH Mobile"
Using saved credentials: xxx@xxx.com
Starting Build in bld
Built: bld\12-jun-search-icon.png.
Built: bld\icons.png.
Built: bld\icons@2x.png.
Built: bld\style.css.
Problem building 'mobify.js':
Error: Failed loading partial: {)"/base\tmpl\base_root.tmpl"}
Built: bld\mobify.js.
There were some errors in the build process.
Removing bld

fs.js:357
return binding.rmdir(pathModule._makeLong(path));
^
Error: ENOTEMPTY, directory not empty 'D:\website\bld'
at Object.rmdirSync (fs.js:357:18)
at Object.rmdirSyncRecursive (C:\AppData\Roaming\npm\node_modules\mobify-client\node_modules\wrench\lib\wrench.js:155:15)
at C:\AppData\Roaming\npm\node_modules\mobify-client\src\commands.coffee:107:18
at C:\AppData\Roaming\npm\node_modules\mobify-client\src\project.coffee:107:11
at Builder.(anonymous) (C:\AppData\Roaming\npm\node_modules\mobify-client\src\build.coffee:553:16)
at Builder.emit (events.js:64:17)
at C:\AppData\Roaming\npm\node_modules\mobify-client\src\build.coffee:505:26
at C:\AppData\Roaming\npm\node_modules\mobify-client\node_modules\async\lib\async.js:94:25
at C:\AppData\Roaming\npm\node_modules\mobify-client\src\build.coffee:496:20
at Stub.callback (C:\AppData\Roaming\npm\node_modules\mobify-client\src\build.coffee:290:13)