Fallback to 127.0.0.1 if localhost is unusable

Fix #937
Config| Fix typo for default_bind_host
Added check to postgres for instance stats and hot_standby replication lag
postgres checks for instance stats and hot_standby replication lag
addition of explicit var names and removal of uneeded loops
updated to reflect replication lag returned as timedelta
removed unneeded use of dictionaries to hold a single metric
removed unneeded use of dictionaries to hold a single metric
TCP Metrics | /proc/net/snmp depends on kernel version
Merge pull request #955 from DataDog/additional_tcp_metrics

TCP Metrics | /proc/net/snmp depends on kernel version
Merge pull request #952 from DataDog/postgresChecks

Added check to postgres for instance stats and hot_standby replication l...
instance_status can be none on first run
Add check warnings and initialization errors
dont use ternary operator
review fix
Merge pull request #956 from DataDog/tristan/checks-review

Add check warnings and initialization errors
Typo
Merge pull request #957 from DataDog/windows_hosts_fix

Windows hosts fix
Docker is not available on Windows
Merge with master