dhcpcd --dumplease without an interface fails to dump all leases

[holmanb]

Per the docs, all interfaces should be dumped:

-U, --dumplease [interface]
         Dumps the current lease for the interface to stdout.  If no interface is given then all
        interfaces are dumped.  

However, that is not the behavior that I observe:

# pgrep -a dhcpcd
73220 dhcpcd: eth0 [ip4] [ip6]
73221 dhcpcd: [privileged proxy] eth0 [ip4] [ip6]
73222 dhcpcd: [network proxy] eth0 [ip4] [ip6]
73223 dhcpcd: [control proxy] eth0 [ip4] [ip6]
73226 dhcpcd: [DHCP6 proxy] fe80::222:48ff:fe2f:d94
73229 dhcpcd: [BPF ARP] eth0 10.0.0.4
73240 dhcpcd: [BOOTP proxy] 10.0.0.4
# dhcpcd --dumplease 
dhcpcd is not running
# pgrep -a dhcpcd
73220 dhcpcd: eth0 [ip4] [ip6]
73221 dhcpcd: [privileged proxy] eth0 [ip4] [ip6]
73222 dhcpcd: [network proxy] eth0 [ip4] [ip6]
73223 dhcpcd: [control proxy] eth0 [ip4] [ip6]
73226 dhcpcd: [DHCP6 proxy] fe80::222:48ff:fe2f:d94
73229 dhcpcd: [BPF ARP] eth0 10.0.0.4
73240 dhcpcd: [BOOTP proxy] 10.0.0.4

I haven't dug into why this happens yet, it's not directly a use case of mine but the fact that the documented behavior is broken is relevant to the two fixes I have for #285 - one fix would break the documented user interface, the other fix would not (but the second fix leaves in place the unreliable "wait on data in the pipe" semantics).

[rsmarples]

This is because you started dhcpcd on eth0 but didn't limit that in your request to dump leases.
Related to #271