rename skip to precondition

[fokion]

In order to skip a test case or a step the assertions of the skip block MUST be false and when we have all the assertions valid under the skip block then it will execute it. This is confusing in my opinion as it is acting as a precondition of our assertions.
I propose to rename this block to precondition and if we want to use the skip field we can convert it so that if everything is asserted as true then it must actually skip it.

[ivan-velasco]

This brings up the question, should there be support in test suites for before and after routines also? At present, I find myself needing to craft a test prior to and following an entire set of tests for setups and teardown routines. You get additional "tests" counted in the final result which can be misleading.
For instance:
Original:

test: get_login_token
test: testcases_to_run
test: remove_tenants

After:

before: get_login_token
test: testcases_to_run
after: remove_tenants

[yesnault]

I'm agree that it can be tricky to well understand the condition skip.

For example:

name: "Skip testsuite"
vars:
  foo: bar

testcases:
- name: testA
  skip: 
    - foo ShouldEqual aaa
  steps:
  - type: exec
    script: echo "it's skipped"

returns:

❯ venom run -vv a.yml
          [trac] writing venom.49.log
 • Skip testsuite (a.yml)
        • testA
                • (all steps were skipped)
final status: SKIP

say that:

• "if one condition from the skip block is not true, it's skipped"

Adding #806 for now.