This addresses GH-5165 and adds the ability to check if a lvol exists.

The tests for this don't fit nicely into the current integration tests so they are below.

```
---

- name: remove any existing lv=one of vg=main
  lvol: lv=one vg=main state=absent

- name: remove any existing lv=two of vg=main
  lvol: lv=two vg=main state=absent

- name: check to see if lv=one of vg=main exists
  lvol: lv=one vg=main state=present
  ignore_errors: true
  register: lvol_result0

- name: Assert that we will get a "No size given."
  assert:
    that:
      - "'No size given.' in lvol_result0.msg"

- name: create lv=one of vg=main sized 30g
  lvol: lv=one size=30g vg=main state=present
  register: lvol_result1

- name: Assert that we made changes."
  assert:
    that:
      - "lvol_result1.changed == True"

- name: check to see if lv=one of vg=main exists
  lvol: lv=one vg=main state=present
  register: lvol_result2

- name: Assert that we did not make changes."
  assert:
    that:
      - "lvol_result2.changed == False"

- name: remove lv=one of vg=main
  lvol: lv=one vg=main state=absent

- name: create lv=two of vg=main sized 30G
  lvol: lv=two size=30G vg=main state=present
  register: lvol_result3

- name: Assert that we made changes."
  assert:
    that:
      - "lvol_result3.changed == True"

- name: reduce lv=two of vg=main to 15G
  lvol: lv=two size=15G vg=main state=present
  register: lvol_result4

- name: Assert that we made changes."
  assert:
    that:
      - "lvol_result4.changed == True"

- name: increase lv=two of vg=main to 30G
  lvol: lv=two size=30G vg=main state=present
  register: lvol_result5

- name: Assert that we made changes."
  assert:
    that:
      - "lvol_result5.changed == True"

- name: create lv=two of vg=main sized 30G when already exists at 30G
  lvol: lv=two size=30g vg=main state=present
  register: lvol_result6

- name: Assert that we did not make changes."
  assert:
    that:
      - "lvol_result6.changed == False"

- name: remove lv=two of vg=main
  lvol: lv=two vg=main state=absent
```