Print the command line and ABI in stack dumps like debuggerd.

Ensure the heading is "Cmd line:" just like debuggerd and
as it used to be in Dalvik.
Fix a missing newline.
Trim all training nulls from the command line.
Don't bother printing the original command line if unset.
Add the ABI to the dump to help the native stack symbol tool.

Bug: 17474152
Change-Id: I19c585dbd7d31ef6c98270e469445cae40cbd518