Previously a bad error code was returned, fixes#1477.
Testing:
I have two test cases to test the solution. The first is a request that
makes depsolve crash by changing the dnf-json script by an almost empty
one that only throws an exception. The second one fails because it
requests a non existing package. The former ends with a 500 error and
the later with a 400.
----8<-----
HTTP/1.1 500 Internal Server Error
Failed to depsolve base packages for ami/x86_64/centos-8: ailed to
depsolve base packages for ami/x86_64/centos-8: unexpected end of JSON
input
----8<-----
HTTP/1.1 400 Bad Request
Content-Length: 226Failed to depsolve base packages for
ami/x86_64/centos-8: DNF error occured: MarkingErrors: Error occurred
when marking packages for installation: Problems in request:
missing packages: jesuisunpaquetquinexistepas_idonotexist
cfc91a3eb6