abort from subshell

- highlight
  - add set -e bofore subshell
  - when you receive output of subshell, do not use local val=$(sub shell), but use local val; val=$(sub shell). 
- test.sh
```
#!/bin/bash

set -e errexit
set -o pipefail

cwd=`dirname $0`
source $cwd/testsrc.sh

digest=$(set -e; testfunc) # use set -e to abort
echo "digest=[$digest]"
```

- testsrc.sh
```
#!/bin/bash

function subtestfunc() {
	exit 1;
}
function testfunc() {
	local ret  # do not directly capture output of subshell
	ret=$(set -e; subtestfunc)
	local ec=$?
	echo "ec=[$ec],ret=[$ret]"
}
```