Making timeout units consistent

[wangvsa]

Current configuration allows setting three timeouts, but they don't use the same unit.

margo section:

• client_timeout: timeout in milliseconds for rpcs between client and server (default: 5000)
• server_timeout: timeout in milliseconds for rpcs between servers (default: 15000)

server section:

• init_timeout: timeout in seconds to wait for servers to be ready for clients (default: 120)

Maybe better to make the three timeout units the same? Probably all use seconds.
Otherwise, It can be confusing when checking a job script with all three environment variables:

export UNIFYFS_SERVER_INIT_TIMEOUT=600
export UNIFYFS_MARGO_CLIENT_TIMEOUT=60000
export UNIFYFS_MARGO_SERVER_TIMEOUT=60000