ovh_domain_zone_record: Make fieldtype non-updatable

[radeksimko]

Tests without patch:

make testacc TEST=./ovh TESTARGS='-run=TestAccOvhDomainZoneRecord_updateType'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./ovh -v -run=TestAccOvhDomainZoneRecord_updateType -timeout 120m
=== RUN   TestAccOvhDomainZoneRecord_updateType
--- FAIL: TestAccOvhDomainZoneRecord_updateType (12.17s)
    testing.go:538: Step 1 error: Error applying: 1 error(s) occurred:

        * ovh_domain_zone_record.foobar: 1 error(s) occurred:

        * ovh_domain_zone_record.foobar: Failed to update OVH Record: Error 400: "Try to alter read-only properties: fieldType"
FAIL
FAIL	github.com/terraform-providers/terraform-provider-ovh/ovh	12.194s
make: *** [testacc] Error 1

with patch:

make testacc TEST=./ovh TESTARGS='-run=TestAccOvhDomainZoneRecord_updateType'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./ovh -v -run=TestAccOvhDomainZoneRecord_updateType -timeout 120m
=== RUN   TestAccOvhDomainZoneRecord_updateType
--- PASS: TestAccOvhDomainZoneRecord_updateType (12.14s)
PASS
ok  	github.com/terraform-providers/terraform-provider-ovh/ovh	12.167s