"pub cache repair" prints a more detailed summary.

"pub cache repair" prints a more detailed summary.

Now instead of just saying how many packages failed to be
reinstalled/reactivated, "pub cache repair" will print a list of those
packages.

This also fixes an issue where "pub cache repair" would incorrectly
return a 0 exit code when packages failed to reactivate.

Closes #1301

R=rnystrom@google.com

Committed: https://github.com/dart-lang/pub/commit/bbe564d5b849b96cf5f86ba39cdea6c46ad62a69

[Bob Nystrom, 2015-07-15 20:22:42]

lgtm

[nweiz, 2015-07-15 20:38:59]

Committed patchset #1 (id:1) manually as
bbe564d5b849b96cf5f86ba39cdea6c46ad62a69 (presubmit successful).