feat(build script): Return exit code

[baleevskiy]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
Return error exit code from the build script in case of error

[rcalimlim]

Hey @baleevskiy just checking in on this PR as it's been out here for over a year. Did you open a feature suggestion and get it approved prior to opening this PR? If so, can you add a test case? Should be straightforward :)

Per the contribution guidelines:

If adding a new feature:

• Add accompanying test case.
• Provide a convincing reason to add this feature. Ideally, you should open a suggestion issue first and have it approved before working on it.