devtools: gosh: switch from Logf/Fatalf to TB, and related

This change makes most of the changes described in the final
proposal in https://v.io/i/1128 - namely, it makes all the
requisite API changes.

Things not done in this change:
- "Good PC" logging
- Printing Cmd stdout/stderr on failure

Those will be done in subsequent changes.

MultiPart: 3/9

Change-Id: Ie6d2e1131cc56c0a5c728cca6cab269f8c2a4d13
diff --git a/exec.go b/exec.go
index e8afec8..b6d913b 100644
--- a/exec.go
+++ b/exec.go
@@ -34,7 +34,7 @@
 }
 
 func runMadbExecForDevice(env *cmdline.Env, args []string, d device) error {
-	sh := gosh.NewShell(gosh.Opts{})
+	sh := gosh.NewShell(nil)
 	defer sh.Cleanup()
 
 	cmdArgs := append([]string{"-s", d.Serial}, args...)
@@ -48,5 +48,5 @@
 	stdout.Flush()
 	stderr.Flush()
 
-	return sh.Err
+	return nil
 }
diff --git a/madb.go b/madb.go
index 45c7c40..c4c2152 100644
--- a/madb.go
+++ b/madb.go
@@ -84,7 +84,7 @@
 
 // Runs "adb devices -l" command, and parses the result to get all the device serial numbers.
 func getDevices(nicknameFile string) ([]device, error) {
-	sh := gosh.NewShell(gosh.Opts{})
+	sh := gosh.NewShell(nil)
 	defer sh.Cleanup()
 
 	output := sh.Cmd("adb", "devices", "-l").Stdout()
diff --git a/start.go b/start.go
index 5287715..3093cf7 100644
--- a/start.go
+++ b/start.go
@@ -33,7 +33,7 @@
 }
 
 func runMadbStartForDevice(env *cmdline.Env, args []string, d device) error {
-	sh := gosh.NewShell(gosh.Opts{})
+	sh := gosh.NewShell(nil)
 	defer sh.Cleanup()
 
 	if len(args) != 2 {
@@ -63,5 +63,5 @@
 	stdout.Flush()
 	stderr.Flush()
 
-	return sh.Err
+	return nil
 }