Add tag filtering support for ELB (#47)

[jckuester]

make testacc TESTARGS='-run=TestAccElb_*'                            
TF_ACC=1 go test $(go list ./...) -cover -v -run=TestAccElb_* -timeout 120m
?       github.com/cloudetc/awsweeper   [no test files]
?       github.com/cloudetc/awsweeper/command   [no test files]
testing: warning: no tests to run
PASS
coverage: 0.0% of statements
ok      github.com/cloudetc/awsweeper/resource  0.004s  coverage: 0.0% of statements [no tests to run]
?       github.com/cloudetc/awsweeper/resource/mocks    [no test files]
=== RUN   TestAccElb_deleteByTags
time="2019-09-22T11:35:23+02:00" level=info msg="This is a test run, nothing will be deleted!"

---
Type: aws_elb
Found: 1

    Id:     foo
    Tags:       [foo: bar] 
    Created:    2019-09-22 09:35:10.33 +0000 UTC

---

---
Type: aws_elb
Found: 1

    Id:     foo
    Tags:       [foo: bar] 
    Created:    2019-09-22 09:35:10.33 +0000 UTC

---

--- PASS: TestAccElb_deleteByTags (100.14s)
=== RUN   TestAccElb_deleteByIds
time="2019-09-22T11:37:10+02:00" level=info msg="This is a test run, nothing will be deleted!"

---
Type: aws_elb
Found: 1

    Id:     foo
    Tags:       [foo: bar] 
    Created:    2019-09-22 09:36:48.4 +0000 UTC

---

---
Type: aws_elb
Found: 1

    Id:     foo
    Tags:       [foo: bar] 
    Created:    2019-09-22 09:36:48.4 +0000 UTC

---

--- PASS: TestAccElb_deleteByIds (139.61s)
PASS

[kadaan]

Thanks for adding the integration tests!