Provide an option to delete the systemvm template

[kiranchavala]

problem

Currently, there is no option to delete the systemvm template

versions

ACS 4.22 and older

The steps to reproduce the bug

1. Have a cloudstack env with a default systemvm template and the systemvm's using the template

2. Register a new systemvm template

3. Try to delete the older systemvm template

Error

4. Try to delete the new systemvm template

Error

...

What to do about it?

Admin user should be able to delete the systemvm template

Currently, the only way delete the system template is from a database query

[weizhouapache]

update template to User, then delete it

it is also supported by API , but not on UI. #8556