Downloader: fix file descriptor leaks

This also fix some strange errors while downloading files: the file is
downloaded correctly but reading it fails later on as the file was not flushed
on disk (not closed).

Change-Id: Ic853773bdbc955b21b8657ca6bdf03494e954656
Fix LMP for SATA

Change-Id: I2125ed8491e08dbc70f9149222ee3697b6f407d8
LAVA-1410: LC: allow PPAs within lava-test-shell dependencies

Following are implemented:

  * LAVA-1503: Formulate the YAML syntax for PPAs / apt sources
  * LAVA-1504: Scripts for adding sources in debian
  * LAVA-1505: Scripts for adding sources in ubuntu
  * LAVA-1507: Scripts for adding gpg keys

Change-Id: Id1d8123d09383211e0772956d0cb3aed28049533
sendchar: default should be false for uboot devices

Change-Id: Ie56679e642a3b5a868bdc2200419ddb1cbfdde45