New summary output.

[xpconanfan]

The current summary log has limited debug information and is in json.

We need to consider what other useful information we can include in the summary log.
Like information on the invocation status, and device monitoring info.

Also consider using a different format so it's possible to stream this file instead of only writing it out in the end.
This will make the summary log more crash proof and takes less memory.

[xpconanfan]

E.g. AndroidDevice should probably dump adb version used in test

[xpconanfan]

Duplicate of #81

[xpconanfan]

Will address the issue raised in #81 in this as well.