support/scripts/pkg-stats: add tilde '~' expansion for pathes

support/scripts/pkg-stats: add tilde '~' expansion for pathes

When the 'nvd-path', 'json' and 'html' are used like this:

  --html ~/foo

then the tilde expansion is properly done by the shell. However, when
they are used like this:

  --html=~/foo

The shell doesn't do the tilde expansion, and pkg-stats doesn't do
it. This commit modifies pkg-stats to ensure that tilde expansion is
done when parsing the 'nvd-path', 'json' and 'html' arguments.

Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
[Thomas: improve commit log]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>