Changes

filesystem: Enforce lower-case hex AID

our utils.b2h() returns values in lower-case hex string notation,
so let's make sure the CardADF and CardApplication AID values are also
stored in lower case notation, othewise the matching baesd on AIDs
returned from the card will not work, specifically as we use uppercase
AIDs in pySim.euicc for CardApplicationECASD and CardApplicationISDR.

Rather than change those two instances, let's solve it in a generic way.

We already do the same for the CardFile.fid member.

Change-Id: Ie42392412d9eb817fbc563d9165faab198ffa7a9