libbe(3): promote dependent clones when destroying an environment

[jwmaag_gmail.com]

Summary

When removing a boot environment iterate over the dependents and
process the snapshots by grabbing any clones. Promote the clones we
found and then remove the target environment.

Test Plan

• create a boot environment be0
• create two boot environments from be0 (be1, be2)
• destroy be0
• destroy be1

• create be1 from be0
• create be2 from be1
• create be3 from be2
• destroy be2, be3, be1

[jwmaag_gmail.com]

update comment

[kevans]

Overall approach LGTM.

lib/libbe/be.c

205

"promote"

223

This initialization should probably be moved down to just before we iterate over the promotelist; once found is set, we're never resetting it back to false.

243

space after if

247

space after if

272

space after while

407

space after if, before opening brace.

sbin/bectl/tests/bectl_test.sh

151

Unwanted trailing space.

[jwmaag_gmail.com]

fix nits, rearrange promote list unique logic

[kevans]

lib/libbe/be.c

250

newentry is leaked here

252

We should check return value of strdup here, too, while we're at it.

[jwmaag_gmail.com]

free newentry when following the dup or error path

[jwmaag_gmail.com]

on allocation failures, set err = enomem and break out of the loop so we clean up any nvlists/zfs handles instead of just returning