Don't run Solaris build for go1.9

.travis.yml

@@ -5,7 +5,7 @@ matrix:
   include:
     - os: linux
       go: "1.9.x"
-      env: RESTIC_TEST_FUSE=0 RESTIC_TEST_CLOUD_BACKENDS=0
+      env: RESTIC_TEST_FUSE=0 RESTIC_TEST_CLOUD_BACKENDS=0 RESTIC_BUILD_SOLARIS=0
 
     # only run fuse and cloud backends tests on Travis for the latest Go on Linux
     - os: linux

run_integration_tests.go

@@ -135,7 +135,12 @@ func (env *TravisEnvironment) Prepare() error {
 				"freebsd/386", "freebsd/amd64",
 				"openbsd/386", "openbsd/amd64",
 				"linux/arm", "freebsd/arm",
-				"solaris/amd64",
+			}
+
+			if os.Getenv("RESTIC_BUILD_SOLARIS") == "0" {
+				msg("Skipping Solaris build\n")
+			} else {
+				env.goxOSArch = append(env.goxOSArch, "solaris/amd64")
 			}
 		} else {
 			env.goxOSArch = []string{runtime.GOOS + "/" + runtime.GOARCH}