always show python-for-android output on failure

[kived]

Buildozer should collect output from p4a and emit it on build failure. This will avoid a common complaint that an app won't build and the output merely states Command failed, which for some can bring back bad memories of Excel error messages such as File not opened. ;)

[tito]

I added a message when any command failed to execute, if the log_level was <= 1, ask for raising it then re-execute the command. If it's log_level > 1, ask the user to check the backlog. And if he want to raise an issue, include the full log as well.

Let's see if we'll have less unmeaning issue.