src/create_disk.sh: change bls-append-except-default seperator

[saqibali-2k]

We have decided to change the seperator used in the
bls-append-except-default-key. We want to add to the changes
in #2854.

[saqibali-2k]

Let's wait for ostreedev/ostree#2605 to merge before merging this. I will not hit auto-merge this time 😅

[saqibali-2k]

Let's wait for ostreedev/ostree#2605 to merge before merging this. I will not hit auto-merge this time

NVM CI on ostreedev/ostree#2605 needs this change to pass - lets merge this.

[dustymabe]

Disclaimer: I haven't followed the minutia of these changes.

Trivial LGTM

[ravanelli]

@saqibali-2k It is already merged, but could you explain why we decided to change it? Is it just a detail or there is some reason?

[saqibali-2k]

We are adding a corresponding change in OSTree that uses the string-list bls-append-except-default specified here. Originally, the format of the key was key1,value1;key2,value2; however, we found it was more clear to do something like key1=value1;key2=value2. We added the change in the OSTree PR linked above, but tests are failing since the bls-append-except-default key set by COSA is incorrect format.