Report errors from subprocesses

[jugglinmike]

While investigating an issue with this project's "import" script, @howard-e found that a process spawned by the script had crashed. Although this exceptional circumstance should be plainly evident from server logs, Howard could only intuit its occurrence indirectly (that is: by interpreting an error which occurred after the script incorrectly assumed the subprocess had exited cleanly).

Whenever a subprocess is created, the parent should account for the possibility that the child does not complete successfully (even if it is only to report the failure and exit).

A cursory review of the source identifies a number of instances of hazardous subprocess management:

$ git grep spawn '**/*.js'
client/tests/util/getPage.js:const spawn = require('cross-spawn');
client/tests/util/getPage.js:        const server = spawn('yarn', ['workspace', serverOrClient, 'dev'], {
server/scripts/import-tests/index.js:const spawn = require('cross-spawn');
server/scripts/import-tests/index.js:    return spawn
server/scripts/import-tests/index.js:    const installOutput = spawn.sync('npm', ['install'], {
server/scripts/import-tests/index.js:    const buildOutput = spawn.sync('npm', ['run', 'build'], {
server/scripts/import-tests/index.js:    spawn.sync('git', ['clone', ariaAtRepo, gitCloneDirectory]);

...so addressing this problem should begin with a formal audit of the project.