[Bash] Fix matching of header parameters

[devnev]

Currently a generated bash client will not append headers as documented:

bash samples/client/petstore/bash/petstore-cli --dry-run --host localhost getPetById a:b
curl  -sS --tlsv1.2   -X GET "localhost/v2/pet/"

This PR fixes the generated client to match Header-Name: Header-Value parameters and add them to the request:

bash samples/client/petstore/bash/petstore-cli --dry-run --host localhost getPetById a:b
curl  -sS --tlsv1.2 -H "a: b"   -X GET "localhost/v2/pet/"

@frol @bkryza @kenjones-cisco

[wing328]

LGTM but I've not tested it locally.