put retry blocks around record creations

VERIFICATION STEPS

- [x] pull down this branch
- [x] point pro gemfile to local path
- [x] In pro, `bundle install`
- [x] start pro
- [x] new project
- [x] 10.20.39.0/24 as the network range
- [x] scan all hosts
- [x] run psexec against all hosts, with msfadmin:msfadmin
- [x] VERIFY no activeRecord errors


# Release

Complete these steps on DESTINATION

## `VERSION`

### Compatible changes

If your change are compatible with the previous branch's API, then increment [`PATCH`](lib/metasploit/credential/version.rb).

### Incompatible changes

If your changes are incompatible with the previous branch's API, then increment [`MINOR`](lib/metasploit/credential/version.rb) and reset [`PATCH`](lib/metasploit/credential/version.rb) to `0`.

- [ ] Following the rules for [semantic versioning 2.0](http://semver.org/spec/v2.0.0.html), update [`MINOR`](lib/metasploit/credential/version.rb) and [`PATCH`](lib/metasploit/credential/version.rb) and commit the changes.

## JRuby
Do not release, broken on travis-CI.

## MRI Ruby
- [x] `rvm use ruby-1.9.3-p547@metasploit-credential`
- [ ] `rm Gemfile.lock`
- [ ] `bundle install`
- [ ] `rake release`