don't depend on python-apt

but use it if available.

If not the Release file is downloaded and parsed manualy.
Compressed Release files are not supported at the moment.

Signed-off-by: Manuel Traut <manut@linutronix.de>
split out fstabentry code into a seperate module

in hdimg.py parted is importet and fstabentry is defined. But the code
that uses the fstabentry class, doesn't need parted. fstabentry is used in
fstab.mako, so python-parted was necessary on the host sytem for no real
technical reason. This patch moves the fstabentry code into a seperate module
and copies it to the target image, etc.

Signed-off-by: Manuel Traut <manut@linutronix.de>
add more verbose warning if python-apt is not available

Signed-off-by: Manuel Traut <manut@linutronix.de>
v0.5.2

Signed-off-by: Manuel <manut@linutronix.de>