Merge branch 'release-1.5.5' into develop

* release-1.5.5:
  Bumping version to 1.5.5
  [EMR] Update create-cluster synopsis
  [EMR] Update the EMRFS bootstrap action name to be 'Setup EMRFS'
  [EMR] Remove create-cluster --applications default value and update EMRFS bootstrap action name
  [EMR] Correct MapR AMI version in create-cluster examples
Expose waiters in the CLI

Add a ``wait`` command to all services that have waiters. For each type of
waiter, a subcommand representing that waiter was added. For example, to wait
for an ec2 instance to reach the running state, the wait command would be
specified as ``aws ec2 wait instance-running``.
Update waiter code based on feedback
Merge pull request #985 from kyleknap/waiters

Expose waiters in the CLI
Revert "Merge pull request #985 from kyleknap/waiters"

This reverts commit 431b6949e68686378226796cace1cfc866f82613, reversing
changes made to 0a5605e3bcf9372b9f92b3b6eae684df7b16b2eb.
Update CHANGELOG with new service features
Simplify DelegationSetId format
Bumping version to 1.5.6
Merge branch 'release-1.5.6'

* release-1.5.6:
  Bumping version to 1.5.6
  Simplify DelegationSetId format
  Update CHANGELOG with new service features
  Revert "Merge pull request #985 from kyleknap/waiters"
  Update waiter code based on feedback
  Expose waiters in the CLI