Add option to delete the emulator after build only if the build did not succeed

[kageiit]

see: https://issues.jenkins-ci.org/browse/JENKINS-15928

This will also add the ability to delete emulator on jobs which use snapshots in case the emulator fails to start (since using snapshots is unreliable at the moment).

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Jenkins » android-emulator-plugin #64 FAILURE
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Jenkins » android-emulator-plugin #69 SUCCESS
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[jenkinsadmin]

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