Add an option to pass environment variables to the start command

.gitignore

@@ -1,3 +1,4 @@
 *~
 .#*
 *.test
+testserver/cockroach-data/

testserver/testserver.go

@@ -230,6 +230,7 @@ type testServerArgs struct {
 	externalIODir               string
 	initTimeoutSeconds          int
 	pollListenURLTimeoutSeconds int
+	envVars                     []string // to be passed to cmd.Env
 }
 
 // CockroachBinaryPathOpt is a TestServer option that can be passed to
@@ -366,6 +367,14 @@ func PollListenURLTimeoutOpt(timeout int) TestServerOpt {
 	}
 }
 
+// EnvVarOpt is a list of environment variables to be passed to the start
+// command. Each entry in the slice should be in `key=value` format.
+func EnvVarOpt(vars []string) TestServerOpt {
+	return func(args *testServerArgs) {
+		args.envVars = vars
+	}
+}
+
 const (
 	logsDirName  = "logs"
 	certsDirName = "certs"

testserver/testservernode.go

@@ -48,6 +48,7 @@ func (ts *testServerImpl) StartNode(i int) error {
 		"COCKROACH_MAX_OFFSET=1ns",
 		"COCKROACH_TRUST_CLIENT_PROVIDED_SQL_REMOTE_ADDR=true",
 	}
+	currCmd.Env = append(currCmd.Env, ts.serverArgs.envVars...)
 
 	// Set the working directory of the cockroach process to our temp folder.
 	// This stops cockroach from polluting the project directory with _dump