Finally, I was able to find a solution for this. I'm posting the result here, just in case that it's useful for someone else in the future ...
The problem was not in initramfs (dracut), but on the fact that /dev/sda2 partition(PV), after I resized it, somehow got 2 partition table signatures.
One was set as a "dos" partition with an offset "0x1fe" and second set as "LVM_member" with an offset "0x8e".
This confused blkid in initramfs, during the initial boot stage, thinking that /dev/sda2 is *not* an LVM_member but rather a simple "dos" partition, hence refused to activate centos/root and centos/swap LVs which were required to boot the machine to the O/S.
What's interesting is that neither fdisk or parted were showing this second signature, however there was a trace of it in the dracut report file (/run/initramfs/rdsosreport.txt), specifically the one below..
+ blkid /dev/sr0: UUID="2016-10-28-12-18-36-00" LABEL="CentOS 7 x86_64" TYPE="iso9660" PTTYPE="dos" /dev/sda1: UUID="a620a180-3a8c-4b5f-ad30-804f131a7261" TYPE="xfs" /dev/sda2: PTTYPE="dos" + blkid -o udev ID_FS_UUID=2016-10-28-12-18-36-00 ID_FS_UUID_ENC=2016-10-28-12-18-36-00 ID_FS_LABEL=CentOS_7_x86_64 ID_FS_LABEL_ENC=CentOS\x207\x20x86_64 ID_FS_TYPE=iso9660 ID_PART_TABLE_TYPE=dos
To fix the problem, I booted the system from a livecd and used "wipefs" utility to erase the problematic signature "dos" and leave only the correct one "LVM_member".
The exact command was: 'wipefs -o 0x1fe -ff /dev/sda2'
[root@localhost ~]# blkid /dev/sr0: UUID="2016-10-28-12-18-36-00" LABEL="CentOS 7 x86_64" TYPE="iso9660" PTTYPE="dos" /dev/sda1: UUID="a620a180-3a8c-4b5f-ad30-804f131a7261" TYPE="xfs" /dev/sda2: UUID="qBSpoz-i0Zq-AwlP-kviR-leui-L9NA-pcjAg1" TYPE="LVM2_member" /dev/mapper/centos-root: UUID="a48af6f8-13d0-4c5d-a772-463b0da63bb1" TYPE="xfs" /dev/mapper/centos-swap: UUID="7f1d19db-1719-4fe8-a816-0a038a70ecde" TYPE="swap"