* Removed obsolete apkindex_files cache testcase (the corresponding
function has been removed in #345 already).
* Fix test_challenge_apk: It failed on Travis, because we're accessing
/etc/abuild.conf, which only exists after initializing the build environment.
It's a random dummy file anyway, so I've replaced it with another file.
* Fix test_folder_size: accept a tolerance in the result
* Automatically compute the minimum size for the partitions
* Automatically resize the pmOS_root partition during the boot process
* Resize root partition only if there is unallocated space at the end of the device.
* Added more echos to make debugging easier while looking at the pmOS_init.log.
* Updated static_code_analysis.sh script to run shellcheck with `-x` option.
