Enable package-management using OPKG

Summary: OPKG based package management enabled by default.

Test Plan:
```
root@bmc-oob:~# opkg install tcpdump_4.9.3-r0_armv6.ipk

Collected errors:
 * Solver encountered 1 problem(s):
 * Problem 1/1:
 *   - nothing provides libpcap1 >= 1.9.0 needed by
     tcpdump-4.9.3-r0.armv6
 *
 * Solution 1:
 *   - do not ask to install tcpdump-4.9.3-r0.armv6

root@bmc-oob:~# opkg install ./libpcap1_1.9.0-r0_armv6.ipk
Installing libpcap1 (1.9.0) on root
Configuring libpcap1.
root@bmc-oob:~# opkg install ./tcpdump_4.9.3-r0_armv6.ipk
Installing tcpdump (4.9.3) on root
Configuring tcpdump.
```

Reviewed By: williamspatrick

fbshipit-source-id: 408b0299a5

meta-facebook/conf/distro/openbmc-fb.conf

@@ -38,10 +38,10 @@ SSTATE_DIR ?= "${COREBASE}/../../../.sstate"
 #TMPDIR = "${TOPDIR}/tmp"
 
 # Use RPM packages
-PACKAGE_CLASSES ?= "package_rpm"
+PACKAGE_CLASSES ?= "package_ipk"
 
 # Extra image features.
-EXTRA_IMAGE_FEATURES = "ssh-server-openssh tools-debug"
+EXTRA_IMAGE_FEATURES = "ssh-server-openssh tools-debug package-management"
 
 # List of supported distros we are using
 SANITY_TESTED_DISTROS += " \
@@ -132,7 +132,7 @@ DEFAULT_TIMEZONE ?= "America/Los_Angeles"
 # Get the OpenBMC verion
 INHERIT += "openbmc_version"
 
-OPENBMC_FB_DEFAULT_FEATURE = "ext2 ipv6 largefile usbgadget usbhost nfs zeroconf package-management ipv4"
+OPENBMC_FB_DEFAULT_FEATURE = "ext2 ipv6 largefile usbgadget usbhost nfs zeroconf package-management"
 OPENBMC_BOARD_FEATURE ?= ""
 DISTRO_FEATURES = "${DISTRO_FEATURES_LIBC} ${OPENBMC_FB_DEFAULT_FEATURE} ${OPENBMC_BOARD_FEATURE}"
 DISTRO_FEATURES_BACKFILL_CONSIDERED = "\

meta-facebook/meta-fby2/meta-fby2-rc/conf/local.conf

@@ -105,7 +105,7 @@ DISTRO ?= "poky"
 #  - 'package_rpm' for rpm style packages
 # E.g.: PACKAGE_CLASSES ?= "package_rpm package_deb package_ipk"
 # We default to rpm:
-PACKAGE_CLASSES ?= "package_rpm"
+PACKAGE_CLASSES ?= "package_ipk"
 
 #
 # SDK target architecture