Add DAP Intro Option for Node Certificate Rotation

[micahlee]

This PR modifies DAP intro in a couple of ways:

• It updates the HAProxy config to support older versions of DAP by using the standard HTTPS port (443) for health checks, rather than rely on the newer HTTP health check on port 444.

• It adds a procedure flag to dap intro to rotate the node certificates called --rotate-custom-certificates. This allows for quickly testing certificate rotation for the Master, Standbys, and Follower in DAP Intro.

Closes #89

To try the new rotation function:

# Provision a Master
bin/dap --provision-master

# Import custom certificates
bin/dap --import-custom-certificates

# Provision Standbys
bin/dap --provision-standbys

# (Optional) Enable Auto-failover
bin/dap --enable-auto-failover

# Provision Follower
bin/dap --provision-follower

# Verify the deployment is working
bin/api --load-policy-and-values
bin/api --fetch-secrets

# Rotate the node certificates
bin/dap --rotate-custom-certificates

# Verify the deployment is still working
bin/api --load-policy-and-values
bin/api --fetch-secrets

[micahlee]

Alright, @h-artzi, this should be ready for another look. Thanks!